1. The Field of the Invention
The present invention relates to a method and apparatus to recycle production well casing steam, thereby providing substantial economic savings while reducing environmental concerns.
2. The Prior Art
Heretofore, in enhanced oil recovery steam floods, a portion of the injected steam traverses the formation and returns to the surface via the production well annulus mixed with distilled hydrocarbons and other compounds from the reservoir. This casing vapor mixture is collected from all the production wells to a central station where it is cooled to liquify for collection of the steam and at least some of the hydrocarbons. The non-condensible vapors have generally been disposed of by incineration. However, these non-condensibles often include hydrogen sulfides, which oxidize to form sulfur oxides, and thus must not exceed maximum acceptable values in order for the resulting flue gas from the incineration to meet environmental standards.
The prior art methods for a steam flood have some economic disadvantages. The steam that returns to the surface is generally treated as a low grade heat source that is not economic to recover or use. In fact energy is expended to condense the steam to allow recovery of the hydrocarbons in the casing vapor mixture. This prior art system of treating the steam portion of the casing vapor mixture as though it was a totally spent product results in substantial loss of heat with no economic advantage being derived therefrom, especially since steam is generally costly to generate. This method of treating the steam as totally used up also has adverse environmental consequences in its disposal.
An example of steam injection into a reservoir for a more complete recovery of the hydrocarbons contained therein can be found in U.S. Pat. No. 3,460,621, the disclosure of which is incorporated herein by reference. It is also known to use at least a portion of the product recovered from the reservoir as a source of energy to continue the production cycle. An example of this can be found in U.S. Pat. No. 4,160,479, the disclosure of which is also incorporated herein by reference. Further, it is known that one problem with steam flooding is maintaining the quality of the steam as this has a direct effect on the amount of heat imparted to the formation by the steam. A system for conserving steam quality is disclosed in U.S. Pat. No. 5,085,275, the disclosure of which is incorporated herein by reference.